1. Technical Field
The invention is in the domain of mobile telecommunications and more specifically relates to a method of automatically indicating available services to a mobile telecommunications terminal roaming between a first geographic area and a second geographic area.
The invention also relates to a telecommunications system in which a mobile terminal is roaming between a first geographic area and a second geographic area.
2. Prior Art
In a cellular telecommunications network, a geographic area comprises a limited number of uniquely identified cells in which the network sends paging messages to determine the location of a terminal in the network and to notify it that a call is being made to it. This message is transmitted through a particular radio message channel called PCH (“Paging Channel”). The GSM-GPRS and UMTS standards define several areas called LAs ((Location Area)) for the circuit domain, and RA (Routing Area) for the packet domain comprising several adjacent cells.
In the circuit switching domain, the location areas LA are managed by the MSC/VLR module comprising the Mobile Service Switching Center switch (MSC), and a Visitor Location Register (VLR) database containing information related to subscribers in standby mode.
In the packet switching domain (GPRS and UMTS), routing areas RA are managed by the Serving GPRS Support Node (SGSN) that is the equivalent of the MSC/VLR module for services in packet mode.
After being registered on the network, a terminal executes an update procedure in the core network of the current area, after each change of the location area. The terminal knows the area in which the current cell is located due to the information broadcast on a beacon channel associated with each cell (BCCH, Broadcast Control Channel).
A telecommunications network knows the services available in a geographic area covering one or several of its cells independently of the radio coverage quality in this area. Availability of these services for a mobile terminal is defined and known statically by the network, independently of the reception quality in this area.
The technical specifications in the 3GPP standard are not sufficient to enable a mobile terminal camping on a cell in a Routing Area (RA) to easily and quickly know the available services in this area without the need for an active search for services.
According to these specifications, the user must make a series of tests to find a service in the area in which he is located after an inter-system transfer or after the terminal has been reinitialised. This generates an unnecessary consumption of available energy.
The purpose of the invention is to enable a user of a mobile telecommunications terminal to easily and quickly know the services available in a roaming area in a cellular telecommunications network in which the terminal has registered after an intercellular or an intersystem (HPLMN or VPLMN) transfer.